Overhead flexible electric conductor

Abstract

An electric conductor suitable for use in an overhead electrical and optical transmission system comprises a layer or layers of helically wound wires, at least one elongate compartment within and extending throughout the length of the conductor and, loosely housed in the elongate compartment, at least one optical fibre ribbon structure comprising a plurality of optical fibres and flexible elongate reinforcing elements of resilient material arranged side by side and embedded in an elongate body of plastics material, each resilient reinforcing element being set in such a form that the ribbon structure follows a path of smoothly curved undulations whose axes of curvature lie parallel to one another and normal to the longitudinal axis of the ribbon structure. If, when the conductor is installed or in service, the undulating ribbon structure is subjected to a tensile force, the ribbon structure will straighten in a lengthwise direction against the action of the undulating resilient reinforcing elements thereby reducing the tensile force otherwise applied to the optical fibres and, when the tensile force is removed, the ribbon structure will return towards its original undulating form.

What I claim as my invention is: 
     
       1. An overhead flexible electric conductor comprising at least one layer of helically wound bare elongate elements of metal or metal alloy, at least one elongate compartment within and extending throughout the length of the flexible conductor and, loosely housed in the elongate compartment, at least one optical fibre ribbon structure comprising a plurality of optical fibres and at least one flexible elongate reinforcing element of substantially resilient material arranged side by side and embedded in an elongate body of plastics material, wherein the resilient reinforcing element of the optical fibre ribbon structure is pre-set in such a form that the ribbon structure as a whole follows a path of smoothly curved undulations whose axes of curvature lie transverse to the longitudinal axis of the ribbon structure and the arrangement being such that if, when the flexible conductor is installed or is in service, the undulating ribbon structure is subjected to a tensile force, the ribbon structure will straighten in a lengthwise direction against the action of the undulating resilient reinforcing element thereby reducing the tensile force otherwise applied to the optical fibres and, when the tensile force is removed, the ribbon structure will return towards its original undulating form. 
     
     
       2. A flexible conductor as claimed in claim 1, wherein the axes of curvature of the undulations in the undulating optical fibre ribbon structure lie parallel to one another and substantially normal to the longitudinal axis of the optical fibre ribbon structure. 
     
     
       3. A flexible conductor as claimed in claim 1, wherein the optical fibre ribbon structure includes at least two elongate reinforcing elements of substantially resilient material uniformly spaced across the width of the ribbon structure. 
     
     
       4. A flexible conductor as claimed in claim 3, wherein the optical fibre ribbon structure includes two flexible elongate reinforcing elements of substantially resilient material, the separate optical fibres being arranged side by side therebetween. 
     
     
       5. A flexible conductor as claimed in claim 1, wherein the flexible resilient reinforcing element of the optical fibre ribbon structure is of metal or metal alloy. 
     
     
       6. A flexible conductor as claimed in claim 1, wherein the flexible resilient reinforcing element of the optical fibre ribbon structure is of a non-metallic resilient material. 
     
     
       7. A flexible conductor as claimed in claim 1, wherein the radius of curvature of each undulation of the undulating optical fibre ribbon structure is not less than 40 mm. 
     
     
       8. A flexible conductor as claimed in claim 1, wherein the elongate compartment is the bore of a substantially circumferentially rigid central core which is surrounded by the layer or layers of helically wound bare elongate elements of metal or metal alloy. 
     
     
       9. A flexible conductor as claimed in claim 8, wherein the central core is a single extruded elongate member having a central bore which constitutes the elongate compartment. 
     
     
       10. A flexible conductor as claimed in claim 9, wherein the single extruded elongate member is of metal or metal alloy. 
     
     
       11. A flexible conductor as claimed in claim 8, wherein the central core is a single elongate member of substantially U-shaped transverse cross-section, the space between the limbs and base of the U constituting the elongate compartment. 
     
     
       12. A flexible conductor as claimed in claim 11, wherein at least one of the limbs of the U is folded inwardly so that the gap between the free ends of the limbs is at least partially closed. 
     
     
       13. A flexible conductor as claimed in claim 8, wherein the central core is a longitudinally extending tape of metal or metal alloy which is transversely folded to form a tube, the abutting longitudinally extending edges of the tape being welded together. 
     
     
       14. A flexible conductor as claimed in claim 8, wherein the central core consists of two separately formed parts comprising an inner solid elongate member of metal or metal alloy having in its outer surface at least one longitudinally extending recess and, surrounding the inner elongate member, a longitudinally applied transversely folded tape of metal or metal alloy, which tape overlies the longitudinally extending recess to form an elongate compartment. 
     
     
       15. A flexible conductor as claimed in claim 14, wherein the inner elongate member of the central core has in its outer surface four circumferentially spaced longitudinally extending recesses which, when surrounded by the transversely folded tape, constitute circumferentially spaced elongate compartments in at least one of which an undulating optical fibre ribbon structure is loosely housed. 
     
     
       16. A flexible conductor as claimed in claim 8, wherein the central core is of substantially circular transverse cross-section. 
     
     
       17. A flexible conductor as claimed in claim 1, wherein those parts of the elongate compartment not occupied by the undulating optical fibre ribbon structure are substantially filled with a water-impermeable medium of such a consistency that the undulating optical fibre ribbon structure is free to move relative to the flexible conductor when the flexible conductor is flexed. 
     
     
       18. A flexible conductor as claimed in claim 1, wherein a layer of thermally insulating material is housed in the elongate compartment and surrounds the undulating optical fibre ribbon structure loosely housed therein. 
     
     
       19. A flexible conductor as claimed in claim 18, wherein the thermally insulating layer in the elongate compartment is a circumferentially continuous layer which is bonded to the boundary surface of the elongate compartment. 
     
     
       20. An overhead electric transmission or distribution system including at least one overhead flexible electric conductor as claimed in claim 1. 
     
     
       21. An overhead electric transmission or distribution system as claimed in claim 20, wherein the overhead flexible electric conductor is an earth conductor of the system.